Lumbar Degenerative Disc Disease (DDD) is easiest described as a wear related condition affecting the discs in your lumbar spine. It is accepted to be very common in adults however it is difficult to speculate its exact occurrence rate due to broad variations in published research. What we do know is that the older we get, the more chance we have of developing it. Although we call it degenerate, advancements in research are now suggesting that nearly three quarters of DDD can actually be attributed to genetic factors. So what it is?
The Anatomy
Intervertebral discs consist of two main sections, an outer annulus, an inner nucleus pulposus and are sealed by 2 endplates, one on the top and one on the bottom. They are sited between the vertebra in our spines separating the large bony areas at the front.
Annulus: This outer structure consists of between 15 to 20 layers of collagen termed lamella, a type of strong inelastic protein similar to those that make up your ligaments. In cross section they look very similar to a sheet of plywood. These are designed in a unique way with each layer running at 120 degrees to compared to the next layer, a structure that has high resistance to tension however a low resistance to compression. Between these layers there is an elastic coating which helps the disc move when under pressure.
Nucleus Pulposus: This viscous liquid similar to the elastic coating in the annulus is like the soft centre of a jam doughnut. It prevents the annulus from collapsing in on its self. A mixture of water (70%), prostaglandin (28%) and collagen (2%) within the nucleus helps to maintain the outward pressure needed for this job. This is essential because like a bicycle tyre, the disc will only operate at its optimum when it is healthy and fully inflated.
Bony End Plates: There are two cartilaginous plates which basically sit on the top and bottom of the individual discs. They are joined at the inner edge of the annulus to the disc and then merge to the bony surfaces of the vertebra above and below. They essentially anchor the disc and keep the annulus and nucleus contents separate from the vertebral body.
The links below help to explin this further.
- Chirogeek - Spineuniverse - Spine Health
How Does It Work?
The role of the disc within the spine is to act as a spacer between the verterbrae and also a shock absorber. The disc undergoes a constant repair/destruct cycle as it absorbs the forces we put through it, a process which is maintained by sufficient delivery in and out of nutrients and metabolic waste. When the balance of this sytem faulters the outward pressure of the disc begins to reduce (like a ballon deflating very slowly) and the annulus begins to loose its normal resistive properties, especially to compressive and torsional forces. This can lead to minor delamination or splitting of the annular rings which, can further alter the discs structural properties and in some cases has the potential to give you pain. These changes would all be placed under the heading of disc degeneration.
In childhood our discs have a blood supply enabling this exchange mechanism to occur effectively however at around the age of 20 years we loose this with the exchange process taking place instead through very small channels in the end plates. Although this system remains effective for the most, it does appear to be more suceptible to failure giving rise to the onset of DDD. This is thought to be why degeneration appears to be far more common in post adoloscence (adulthood), increasing in commmanality with age. For alternative descriptions and animations relating to DDD please follow the links below.
- allaboutbackandneckpain - Spinehealth - Medicinenet
- DDD - Spinehealth
There are some examples where degenerative related back pain occurs in people far younger than you would expect and even seems to run in family lines. Research in recent years, much of which is still ongoing and in its infancy, is suggesting that genetics may play an important role in this. Clinicans who have been involved with assessing and treating back pain have been suggesting the involvement of genetics for years but until recently the technology to investigate this was not sufficient.
The main symptoms of DDD are a continual dull aching local to the lower back and there may be some referral to the top of the buttocks or hips but rarely further. If symptoms do increase, it is likely to be due a separate structure however it is possible that this secondary structure has been disadvantaged or overloaded as a result of the DDD. This differentiation needs skill and should be left to your surgeon or experienced therapist. The only way to clearly identify the presence and level of DDD is by MRI scan an example of which can be seen below.
It is very important to appreciate that not everybody will be suitable for, or need an MRI scan for certain types of LBP. It is estimated that approximately 30% of the whole UK population, if scanned would have clinically significant changes to their spine however many of these would not have, nor ever did, and may never have any symptoms at all. It is very important to appreciate that it is normal not to be perfect! We all undergo ‘wear and tear’ and this should not be feared. It should be left your clinician or surgeon as to whether these investigations are necessary or if the results are realted to your problems at all.
(spine spinal nick birch sciatica slipped disc herniation back pain DDD)
